I. Field of the Invention
The present invention relates to fluid flowmeters, and more particularly to vortex flowmeters of the type including a bluff body disposed in a flow conduit.
II. Description of the Prior Art
Vortex flowmeters are now well known. They are based on the observation that an obstruction placed in a linear flow of fluid produces a plurality of vortices, shed downstream from the obstruction. The vortices create localized oscillatory variations in observable flow parameters such as pressure or velocity. The vortex flowmeter, in its simplest form, thus comprises a flow conduit, an obstruction disposed in the conduit, and a parameter sensor positioned within the conduit at a location where it can be influenced (directly or indirectly) by the vortices. It is well known that, in order to obtain a useful pattern of vortices, a linear run of conduit must be provided both upstream and downstream of the obstruction and sensor, free of any valving, turns or the like. Typically, this linear run extends a few tens of conduit diameters upstream of the sensor and obstruction, and a few conduit diameters downstream of the sensor. The conduit diameter is, of course, uniform over the linear run.
A variety of such vortex flowmeters are known. Variations between the types of meters involve the shape of structure of the obstruction, commonly called a "bluff body", and the location or structure of the sensor. A bluff body is referred to in the art as "cylindrical" when it is elongated and possesses a substantially uniform cross section taken in a direction transverse to the elongation. It is thus understood in the art that the word does not specifically denote a circular cylinder; rather, it is prefaced with a word denoting the shape of the cross section, for example, a "square" cylinder.
Commonly, the bluff body includes a portion which can be referred to, for the sake of simplicity, as an upstream face. The upstream face is adapted to shed vortices at its most widely separated transverse edges when a fluid flow impinges upon the upstream face from an impingement direction perpendicular to the face. The bluff body also commonly includes a downstream portion which is disposed opposite the upstream face, and which faces the stream of vortices formed or shed by the impingement of fluid upon the upstream face. The downstream portion thus generally faces the parameter sensor. The sensor can be any one of several well-known piezoelectric devices.
While prior vortex flowmeters have functioned adequately for their intended purpose, their use has entailed some drawbacks. The prior vortex meters are structurally complex yet relatively fragile devices. The known vortex meters have thus been high in cost, while subject to damage from vibration during use. They have generally been constructed from materials not particularly resistive to hostile fluid, for example, acids, corrosives, or solvents.
Moreover, in practice many prior bluff body meters have been wafer-type devices, generally configured as relatively flat disks sandwiched between segments of the fluid conduit. The diameter of such a disk is typically slightly larger than the diameter of the conduit. In view of the limitations imposed by this structural arrangement, such meters have been useful only in conduits having a diameter of at least (and typically greater than) several inches.
Further, the prior vortex meters have been subject to the same likelihood for improper installation as other types of unidirectional flowmeters. It is estimated that about ten per cent of all flowmeters installed by inexperienced installers are initially incorrectly installed backwards in the associated conduit. This error is most often discovered only when the fluid circuit is actuated and the meter is observed to be inoperable. The result is an increase in the expense of flow measurement, due to damage to the meter and the time wasted in discovery and rectifying the improper installation.